<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>brock</title>
    <style>
        .father {
            width: 80%;
            height: 1000px;
            background-color: pink;

        }

        .son {
            width: 200px;
            height: 200px;
            text-align: center;
            background-color: gray;
            position: absolute;
            left: 50%;
            transform: translate(-50%, 0);
        }
    </style>
</head>
<body>
<div class="father">
    <div class="son">aaa</div>
</div>
</body>
</html>